I have created a URL rewrite with the path ID "home" for my first store view, but when I want to do it with my second store view, it says that the path ID have already been used. Can I use another path ID or what should I do?
Path IDs have to be unique, otherwise how would your system know where to redirect the end-user? You only choice (to my knowledge) would be to use subdomains for each of your store views.
This way, you would be able to define the same "pathID" for different subdomain via a .htaccess. It might be doable via Magento's URL rewrite, but I wouldn't bet on that.